Dc voltage regulator circuit

ABSTRACT

A circuit in which the voltage derived from a reference diode or silicon zener diode is fed back through an emitter-follower circuit to the base of a transistor and the constant current flowing through the emitter-collector circuit of the transistor is in turn applied to the reference diode so that such a stabilized output voltage as cannot be attained by the zener diode alone may be obtained.

United States Patent [191 Sugano et al.

[ 1 June 26, 1973 DC VOLTAGE REGULATOR CIRCUIT Inventors: HitoshiSugano; Akio Tanaka, both of Takatsuki, Japan Assignee: MatsushitoElectronics Corporation,

Osaka, Japan Filed: Mar. 8, 1972 Appl. No.: 232,792

Foreign Application Priority Data Mar. 15, 1971 Japan 46/14481 US. Cl.323/22 T, 323/1, 323/38 Int. Cl. G05f 1/56 Field of Search 307/297;323/1, 4,

References Cited UNITED STATES PATENTS 5/1971 Avins 307/297 3,652,9223/1972 l-lealey et al. 323/22 T OTHER PUBLICATlONS Kesner, Hold ThatVoltage, Motorola Monitor, Vol. 7, No. 3, November, 1969, pages 33-35.

Primary Examiner-A. D. Pellinen Attorney-S. Delvalle Goldsmith, LesterHorwitz et a1.

[57] ABSTRACT 5 Claims, 2 Drawing Figures PAIENIEDJUHZB 191s 3.742.338

FIG.

PRIOR ART DC VOLTAGE REGULATOR CIRCUIT The present invention relates toa dc voltage regulator circuit which is connected to a dc power supplyand which delivers a stabilized output to a load connected thereto evenif there is a variation in the voltage of the dc power supply or in theload.

In a transistorized electronic circuit there is need for a power supplyas a bias voltage source which can supply a constant output voltageirrespective of the variation in the voltage of the power supply or inthe load connected thereto.

For a better understanding of the invention reference may be had to theaccompanying drawings in which the same reference numerals are appliedto like parts or circuit elements and in which:

FIG. 1 shows a conventional regulator circuit for constant voltagesupply; and

FIG. 2 shows a dc voltage regulator circuit according to the invention.

In FIG. 1 which illustrates a prior-art regulator circuit, numerals 1,2, 3, 4, and 6 respectively designate a terminal connected to a powersupply (not shown), a zener diode, a resistor for conducting current tothe zener diode, a transistor in emitter-follower configuration, anemitter resistor for the transistor and an output terminal.

In this circuit, current is drawn through the resistor 3 to the zenerdiode 2. Consequently, a constant voltage is developed across the zenerdiode 2, and the constant voltage available at a point a in FIG. 1 isput out through an emitter-follower circuit consisting of the transistor4 and the resistor 5.

Now, even though there is a variation in the voltage applied to theterminal 1 and therefore a variation in the current flowing through theresistor 3, the variation will be absorbed by the diode 2 which has azener characteristic, so that the change in the voltage at the point ais suppressed.

Further, even if the current drawn from the terminal 6 is changed due tothe variation in the load connected to the terminal 6, the change involtage at the terminal 6 will be suppressed due to the function of theemitterfollower circuit consisting of the transistor 4 and the resistor5.

As seen from the foregoing description, with the conventional regulatorcircuit, the variation in the output voltage due to the variation in thevoltage of the power supply or in the connected load can indeed besuppressed, but, strictly speaking, there will be a variation, thoughvery small, in the output voltage if there is a variation in the powersupply voltage.

Namely, if current flowing through the zener diode is changed, thechange in the zener voltage necessarily ensues which is normally verysmall. As a result, the voltage at the point a and the output voltageavailable at the terminal 6 vary.

The present invention has been made to solve the problem just mentionedwhich is often raised with the prior-art regulator circuit, and it ischaracterized by a circuit for supplying current for the zener diodewhich current is not affected by the variation in the power supplyvoltage, the circuit being able to deliver a stabilized output voltage.

The present invention will now be described by way of example shown inFIG. 2 of the attached drawings.

In FIG. 2, circuit elements designated by numerals 1,

2, 4 and 6 are similar to those indicated by the same numerals in FIG.1; resistors 7 and 8 divide the voltage across a zener diode 2; atransistor 9 and a resistor 10 constitute an emitter-follower circuit; atransistor 11 forms a circuit for delivering a constant current by usingthe voltage available at the emitter of the transistor 9 as base biasvoltage of the transistor 11; resistors 12 and 13 serve respectively asthe emitter and collector resistors for the transistor 11; a diode 14 isinserted for temperature compensation; a transistor 15 and a resistor 16form a circuit for supplying a constant current for the zener diode 2;and a resistor 17 conducts the initial current to the zener diode 2. Theoperation of this circuit to obtain a stabilized output voltage is asfollows.

When a dc voltage from a power supply (not shown) is applied to theterminal 1, current is drawn to the zener diode 2 through the resistor17, so that a reference voltage appears at the point b in the emittercircuit of the emitter-follower transistor 4. The voltage at the point bis then applied as bias voltage to the base of the constant currentconducting transistor 11 through the emitter-follower transistor 9.Current will flow also through the transistor 15 at the same time.

In this way, immediately the voltage is applied to the terminal 1, acircuit is established which leads current to the zener diode 2 throughthe transistor 15.

Since the base bias voltage of the transistor 11 depends on the zenervoltage of the diode 2, the collector current of the transistor 11 iskept constant, and since the base bias voltage of the transistor 15 alsodepends on the constant current, the collector current of the transistor15 and therefore the current to the zener diode 2 is kept constant.

Therefore, the zener voltage of the reference diode 2 is scarcelyaffected by the variations in current and voltage but assumes a constantvalue. Consequently, the output voltage appearing at the terminal 6 willnot fluctuate notwithstanding the variation in the voltage of the powersupply so that a very stable power source can be provided.

It should here be noted that the initial current conducting resistor 17in the circuit shown in FIG. 2 plays a very important role.

Namely, without the resistor 17 no voltage would appear at the point band no collector currents would flow through the transistors 11 and 15since even if a voltage is applied to the terminal 1 no current can flowthrough the zener diode. And therefore no output could be derived fromthe output terminal 6. Thus, the resistor 17 serves to conduct theinitial current to the reference diode, i.e., silicon zener diode 2, andis considered to be an indispensable circuit element. The value of theresistance which the resistor 17 is to possess, must be very carefullychosen.

Namely, if the resistance value of the resistor 17 is small andtherefore if current drawn to the zener diode 2 through the resistor 17is large, it would be difficult to obtain a highly stabilized outputvoltage.

Therefore, the resistance value of the resistor 17 should be so chosensuch that the current flowing through the resistor 17 may besufficiently small in comparison with the collector current of thetransistor 15.

It is needless to say that in this case the current flowing through theresistor 17 must have at least such a value as can produce an outputvoltage at the terminal 6 when a voltage is applied to the terminal 1.

As has hithereto been described, the output of the dc voltage regulatorcircuit according to the invention is not affected by the variation inthe voltage of the power supply connected thereto and therefore iseffectively used to supply a constant voltage for a transistorizedelectronic circuit.

We claim:

1. In combination with a voltage regulator having an emitter followerconnected between input and output terminals and a zener diode connectedto the base of the emitter follower to maintain a substantially constantbase voltage, means for stabilizing the voltage at the output terminal,comprising a current control transistor having an input base and anoutput collector connected to the zener diode for controlling the supplyof base current to the base of the emitter follower, bias voltagecontrol means connected to the input base of the control transistor formaintaining said base current constant, means connected to the outputterminal for supplying a reference voltage to the bias voltage controlmeans, and initial current conducting means connecting the inputterminal to the base of the emitter follower for instantaneouslyrendering the emitter follower conductive to establish said referencevoltage.

2. The combination of claim 1 wherein said reference voltage supplymeans comprises a voltage divider connected to the output terminal, andan emitter follower circuit connecting the voltage divider to the biasvoltage control means.

3. The combination of claim 2 wherein said bias voltage control meanscomprises a constant current conducting transistor having collector andemitter circuits connected in parallel with said emitter followercircuit and a base connected to an output of the emitter fol lowercircuit, the collector circuit of the constant current conductingtransistor being connected to the input base of the control transistor.

4. The combination of claim 3 wherein said initial current conductingmeans comprises a resistor connected to the input terminal.

5. A dc voltage regulator comprising power supply and output terminals,a first transistor having a collector and an emitter connectedrespectively to said power supply terminal and said output terminal anda base, a reference diode connected between the base of said firsttransistor and ground, parallel circuits consisting of a resistor and asecond transistor, said parallel circuits being connected between thepower supply terminal and the base of said first transistor, a voltagedivider circuit connected in series with the emitter of said firsttransistor, a third transistor having an emitter, a collector connectedto the power supply terminal and a base connected to said voltagedivider circuit, the output from the emitter of said third transistorbeing coupled to the base of said second transistor to control base biasvoltage applied to said second transistor.

1. In combination with a voltage regulator having an emitter followerconnected between input and output terminals and a zener diode connectedto the base of the emitter follower to maintain a substantially constantbase voltage, means for stabilizing the voltage at the output terminal,comprising a current control transistor having an input base and anoutput collector connected to the zener diode for controlling the supplyof base current to the base of the emitter follower, bias voltagecontrol means connected to the input base of the control transistor formaintaining said base current constant, means connected to the outputterminal for supplying a reference voltage to the bias voltage controlmeans, and initial current conducting means connecting the inputterminal to the base of the emitter follower for instantaneouslyrendering the emitter follower conductive to establish said referencevoltage.
 2. The combination of claim 1 wherein said reference voltagesupply means comprises a voltage divider connected to the outputterminal, and an emitter follower circuit connecting the voltage dividerto the bias voltage control means.
 3. The combination of claim 2 whereinsaid bias voltage control means comprises a constant current conductingtransistor having collector and emitter circuits connected in parallelwith said emitter follower circuit and a base connected to an output ofthe emitter follower circuit, the collector circuit of the constantcurrent conducting transistor being connected to the input base of thecontrol transistor.
 4. The combination of claim 3 wherein said initialcurrent conducting means comprises a resistor connected to the inputterminal.
 5. A dc voltage regulator comprising power supply and outputterminals, a first transistor having a collector and an emitterconnected respectively to said power supply terminal and said outputterminal and a base, a reference diode connected between the base ofsaid first transistor and ground, parallel circuits consisting of aresistor and a second transistor, said parallel circuits being connectedbetween the power supply terminal and the base of said first transistor,a voltage divider circuit connected in series with the emitter of saidfirst transistor, a third transistor having an emitter, a collectorconnected to the power supply terminal and a base connected to saidvoltage divider circuit, the output from the emitter of said thirdtransistor being coupled to the base of said second transistor tocontrol base bias voltage applied to said second transistor.